Honestly, I wouldn't get them unless you are going to build a really big rig. The GM 2.5 tons are third member axles, not Rockwell Toploaders so you are going to have the same low clearance of any other axle. Parts are difficult to find for them such as lockers and such. They are heavier then sin also, so you are going to have a lot of dead weight under the rig. Make sure you get the transfer case also that you mentioned as the front axle spins in reverse so its useless without it.
Good luck with whatever you do.